1. Field of the Invention
The present invention pertains to methods and systems for measuring the polytropic or isentropic compression exponent, the compressibility factor, the molecular weight and the pseudo-critical pressure and temperature for gases.
2. Background
In gas compression and process operations it is important to know the properties of gases such as the so-called polytropic compression exponent and, particularly, the isentropic exponent, the compressibility factor and the molecular weight of the gas or gas mixture. These properties are widely used in gas compression and transport applications for adjusting compressor operating characteristics, defining the heating value of gases, for example, and determining the amount of gas handled in transport and custody transfer applications.
Although these properties can be determined by laboratory analysis of samples of the gas in question, such processes are time-consuming and the properties of the gas may change between the time of sampling and obtaining measurement results. Accordingly, it has become increasingly evident that a type of "on-line" measurement method and system for determining the above-mentioned gas properties is particularly important. The present invention provides unique methods and systems for determining these gas properties in the so-called on-line manner.